JPH09291974A - High performance automobile drive shaft excellent in torsional fatigue characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high performance automobile drive shaft to improve torsional fatigue characteristics on a whole of a part by improving the torsional resisting fatigue characteristics of the weld part of a balance weight to which a problem occurs especially when the decrease of the weight of an automobile drive shaft is progressed. SOLUTION: In a drive shaft to which a balance weight to reduce the occurrence of centrifugal whirling is attached through projection welding and which transmits the engine drive force of an automobile to wheels, by setting the diameter of the projection of the balance weight to 1.5-4.0mm, a high performance automobile drive shaft is provided to have excellent torsional fatigue characteristics even after mounting of the balance weight.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive shaft for transmitting engine propulsive force to each wheel of a vehicle belonging to a so-called automobile such as a passenger car, a truck and a tractor, for example, a part such as a prober shaft and a drive shaft. The present invention relates to an automobile drive shaft that has improved fatigue characteristics compared to conventional products and that can be reduced in weight due to size reduction.

[0002]

2. Description of the Related Art As described in the Automotive Engineering Handbook (4th volume, Production / Quality / Maintenance p233 Automobile Manufacturers Association, 1991), it is important for a vehicle drive shaft to have little vibration during high-speed rotation. Is one of. As a countermeasure against this, as shown in the external view of the driving component in which the joint component 4 is joined to the steel pipe 1 in FIG. 1 via the joint component joining portion 3, the balance weight 2 is attached to the steel pipe 1 to adjust the weight balance in the circumferential direction. Is done.

The method of attaching the balance weight 2 is roughly classified into two types, that is, (a) spot welding and (b) projection welding shown in FIG. 2, and the driving force is repeatedly transmitted by either method. When a torsional fatigue test corresponding to that is performed, fatigue cracks 6 from the welded portion of the balance weight may be recognized as shown in FIG. 3 (a). In the case of a fatigue test of a low-strength material having a tensile strength of less than 500 MPa, the fatigue crack 7 from the joint part 3 of the joint part determines the characteristics as shown in FIG. As shown in FIG. 3 (a), the fatigue fracture when the material strength is increased and the cross-sectional area of the drive shaft is reduced to reduce the weight as described in the publication is governed by the fatigue crack 6 from the balance weight weld. This is a major obstacle to reducing the weight because the torsional fatigue characteristics deteriorate.

[0004] The main causes of fatigue cracking from a balance weight weld are stress concentration due to the geometrical shape of the weld, changes in the metal structure due to rapid heating and rapid cooling during welding, and the like.
Welding residual stress can be considered. In order to solve these problems, for example, Japanese Unexamined Patent Application Publication No. 6-246440 discloses a manufacturing method in which the fatigue characteristics are improved by heating a balance weight mounting portion. Further, Japanese Patent Laid-Open No. 6-2
Japanese Patent No. 46439 discloses a vehicle drive shaft having excellent torsional fatigue characteristics in which balance weights are attached using arc welding without using conventional spot welding or projection welding as an attachment method, and JP-A-6-249291. Japanese Unexamined Patent Publication (Kokai) discloses an automobile drive shaft which is equipped with a balance weight using an adhesive and has excellent torsional fatigue characteristics.
However, in these inventions, the productivity is reduced in the conventional balance weight mounting process, and the equipment and process need to be changed or newly installed, which has a disadvantage in terms of economy.

In general balance weight mounting, first, the balance weight mounting position is calculated with a balancer,
The balance weight is attached by spot welding or projection welding, and then the balancer is used again to confirm whether the rotational center of gravity of the drive shaft is at a predetermined position. In the current process, for example, Japanese Patent Laid-Open No. 6-246440.
In order to apply the manufacturing method of the publication, it is necessary to newly provide a heating line, and to apply the invention of JP-A-6-246439, it is necessary to change the welding machine. In applying the invention of JP-A-6-249291,
In order to confirm the position of the center of gravity of rotation after mounting the balance weight, it is necessary to dry the adhesive, which causes a problem of lowering productivity.

[0006]

In view of the above situation, the present invention provides a balance weight welded portion with high torsional fatigue resistance that can be manufactured without requiring a large change in the conventional manufacturing process, and as a whole component. The present invention aims to obtain a vehicle drive shaft having high torsional fatigue resistance, and particularly to provide a vehicle drive shaft having high torsional fatigue resistance in a vehicle drive shaft using projection welding as a balance weight mounting method. It is a thing.

[0007]

As a result of various studies on the above problems, the inventors of the present invention have found that a solution can be achieved by setting the dimension of the balance weight projection to a predetermined size. I found it. The gist of the present invention is as follows.

In the drive shaft for transmitting the engine propulsive force of the automobile to the wheels, in which the balance weight for reducing the whirling is attached by the blast welding, the diameter of the balance weight projection is 1.5 mm or more, 4 A high-performance automobile drive shaft with excellent torsional fatigue characteristics, which is characterized by being less than 0.0 mm.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the main causes of fatigue cracking from a balance weight weld are stress concentration due to the geometrical shape of the weld, and changes in the metal structure due to rapid heating and quenching during welding. And welding residual stress. Of these factors, the present inventors have the greatest effect on the fatigue properties of the balance piece weld,
Based on this idea, the shape and size of the projection 8 of the balance weight was examined in order to improve the geometric shape of the projection welded portion and reduce the stress concentration. For the shape, see Fig. 4.
As shown in (a) to (c), a balance weight 2 having a projection shape such as (a) hemispherical shape, (b) truncated cone shape, (c) columnar shape, etc. is produced, and this is used as a drive shaft. A torsion fatigue test was carried out after mounting, but there was no particular difference in fatigue characteristics due to shape. However, the influence of the size was great, and when the diameter of the projection was less than 4.0 mm, the fatigue characteristics were improved. The diameter of the projection referred to here is d shown in FIGS. 4 (a) to 4 (c). When the diameter of the projection is 4.0 mm or more, there is almost no effect of the diameter of the projection, and the fatigue strength is low and almost constant. The fatigue property is improved as the diameter of the projection is smaller, but if it is less than 1.5 mm, a problem occurs in the joint strength of the projection welded portion.
That is, when the balance weight is pressed and fixed onto the drive shaft before energization, the projection is crushed and the welding becomes unstable, or the heat capacity of the projection part is extremely smaller than that of the drive shaft part. As a result, a phenomenon such that sufficient melting on the drive shaft side cannot be obtained occurs, and the joint area itself decreases due to the reduction in the projection diameter, and the joint strength declines and is subject to repeated twisting. This causes the inconvenience that the balance weight is deviated. For the above reasons, in the present invention, the range of the projection diameter is set to 1.5 mm or more and less than 4.0 mm.

Further, as described above, since there is no difference in fatigue characteristics depending on the shape of the projection (hemispherical type, truncated cone type, columnar type, etc.), the fatigue strength is limited by limiting the projection diameter. The scope of the present invention in which is improved is not limited by the shape of projection. That is, whatever the shape of the projection is used, it is essentially within the scope of the present invention that the diameter of the projection is optimized to improve the fatigue strength.

Height of projection (FIG. 4 (a),
Regarding h) in (c), the scope of the present invention is not particularly limited. According to the study of the present inventors, since the influence of the projection height on the fatigue characteristics is not particularly observed, the dimension may be appropriately selected so that the projection welding can be stably performed.

In the attachment of the balance weight by the projection welding, it is general that a plurality of projections are provided on one balance weight to perform simultaneous multi-point welding. The present invention is applicable to such multi-point welding. Is also applicable. That is, even in a balance weight having a plurality of projections, the fatigue characteristics can be improved by setting the diameter of each projection within the dimensional range of the present invention.

[0013]

[Example] A balance weight having various projection shapes and dimensions is projection welded to a drive shaft having a high-strength steel pipe portion having an outer diameter of 114.3 mm, a wall thickness of 4.0 mm, and a tensile strength of 735 MPa class. And a torsional fatigue test was carried out. Two projections were provided on one balance weight, and two-point stop welding was performed. The results are shown in Table 1. In Comparative Examples 10 to 12 in which the projection diameter was less than 1.5 mm, the projection welding was unstable and a good joined state could not be obtained. FIG. 5 shows the results of Table 1 as a relation between the projection diameter and the breaking life. In all cases, the fatigue crack was a fatigue crack from the mounting portion of the balance weight, but as shown in Table 1 and FIG. 5, in the invention examples 1 to 9 in which the projection diameter was less than 4.0 mm, An improvement in fracture life is observed regardless of the projection shape.

[0014]

[Table 1]

[0015]

EFFECTS OF THE INVENTION According to the present invention, in a vehicle drive shaft in which balance weight for reducing whirling is attached by projection welding, fatigue fracture from the balance weight attachment portion which has deteriorated torsional fatigue characteristics. The generation can be delayed, and the torsional fatigue characteristics of the component can be improved. As a result, the stress in actual use can be increased, and the weight of the automobile propulsion shaft can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing the structure of a typical automobile drive shaft.

FIG. 2 is a diagram showing an outline of spot welding (a) and projection welding (b) for attaching a balance weight to a drive shaft.

FIGS. 3 (a) and 3 (b) are diagrams showing fatigue fracture occurrence positions when a torsional fatigue test, which is a main performance evaluation, is performed on a drive shaft.

FIG. 4 is a diagram showing the shape and dimensions of a balance weight projection, in which (a) is a hemispherical projection;
(B) is a figure which shows a truncated cone type projection, and (c) is a columnar type projection.

FIG. 5 is a view showing a relationship between a projection weight diameter of a balance weight and a breaking life in a torsional fatigue test.

[Explanation of symbols]

 1 Steel pipe 2 Balance weight 3 Joint part joint 4 Joint part 5 Electrode tip 6 Balance weight Fatigue crack from weld part 7 Fatigue crack from joint part joint 8 Balance weight projection (projection) d Projection diameter h Projection height

Claims (1)

[Claims] 1. A drive shaft for transmitting an engine propulsion force of an automobile to a wheel, wherein a balance weight for reducing whirling is attached by projection welding, wherein a balance weight has a projection diameter of 1.5 mm.
As described above, a high performance automobile drive shaft having excellent torsional fatigue characteristics, which is less than 4.0 mm.